The present invention relates to electrical parts, for example, they are dielectric antenna, such as a microwave antenna used for mobile communications and walkie-talkies; condensers, filters, and printed circuit substrate for the high-frequency range of microwaves or higher frequency. In addition, the present invention relates to a manufacturing method for the above mentioned electrical parts, such as an antenna.
Further, the present invention relates to a dielectric ceramic suitable for dielectrics of such electrical parts, and resin-ceramic composite material.
As a conventional material for a microwave antenna, a condenser, a filter, and a printed circuit substrate for high-frequency use, ceramics made by baking are mainly used. The baked ceramics have an advantage that they can attain a high dielectric constant (∈) and a low dielectric dissipation factor (tan xcex4), compatibly. However, the conventional material is never free from an antinomic relation that a composition whose change in dielectric constant owing to change of temperature (i.e. temperature dependence) is small, causes a low dielectric constant. Further, the baked ceramic material has defects that they require a baking step to be conducted at a temperature above 1,000xc2x0 C., they have difficulty in post-processing, because of hardness and brittleness, and they have difficulty in post-forming a metal pattern (the pattern is formed by means of converting a paste of a metal, such as silver, drawn in a pattern beforehand, into a metal itself, at the baking step).
On the other hand, a composite material, comprising a resin blended with a ceramic powder, has been developed (for example, JP-A-8-69712 (xe2x80x9cJP-Axe2x80x9d means unexamined published Japanese patent application)). The composite material obtained in this way has an advantage of being readily processable (i.e. a general method for molding resins can be employed). However, the dielectric constant generally decreases when a ceramic is powderized. As such, the conventional composite material blended with a ceramic powder has a disadvantage of a low dielectric constant.
Further, there is a problem in the composite material that, when a conventional ceramic with a high dielectric constant is employed, to raise the dielectric constant of a composite material, the temperature dependency of dielectric constant of the composite material increases, as in the case of the said baked ceramic. On the other hand, when a ceramic with a large particle size, or a fiber-shaped ceramic, is used for the purpose of maintaining a dielectric constant as high as possible, the composite material becomes inferior in formability and difficulty of forming a minute metal pattern when used for a printed circuit substrate.
Additionally, a resin-ceramic composite material, using polyphenylene sulfide (PPS) as a resin, is described in JP-A-9-36650. The PPS is highly evaluated for its low tan xcex4. However, an investigation by the present inventors revealed that there was still room to reduce changes of characteristics by moisture absorption. Namely, it was found that reduction of the changes of tan xcex4 and ∈ by moisture absorption was desirable. However, these points were not studied in the above-mentioned JP-A-9-36650.
In addition, as PPS was a resin hard to plate thereon, because it had high chemical resistance and therefore it exhibited low adhesion strength to adhesives. As such, the use of a resin-ceramic composite material using PPS for electrical parts, such as a dielectric antenna, has been very limited.
To solve this kind of problem, a method of using a ceramic powder with a limited particle size, ranging from 1 to 10 xcexcm, and plating the obtained PPS resin composition, after a surface treatment, by wet etching with solvent or solution, is disclosed in JP-A-61-183473. However, a wet etching has a disadvantage in cleaning, after the treatment was performed. In addition, a solvent that can etch PPS is extremely limited to specific ones, and such special solvents are not good for workers, because of harmful effects on the human body and a foul odor. In JP-B-56-25453 (xe2x80x9cJP-Bxe2x80x9d means examined published Japanese patent application), a method, in which plating is carried out after physical etching and a modification of PPS surface by a treatment with an oxidizing solution, is also disclosed. However, there is the same problem as above because the oxidizing solution is also extremely limited to such specific solutions.
The above-mentioned and other and further features, and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawings.